This invention relates to the processing of aluminum parts and, more particularly, to the stabilization of the surface of aluminum lead frames for semiconductor devices.
In the assembly of semiconductor devices, a lead frame which provides a mounting for the semiconductor chip, plus electrical terminals for the completed device is utilized. Typically, the lead frame is of aluminum or is aluminum surfaced because the metallization on the semiconductor chip is of aluminum, thus an aluminum wire is used to bond between the electrical contact pads on the chip and to the aluminum or aluminum coated lead frame without the electromigration problems that might be associated with the utilization of dissimilar metals. Prior to the bonding between the chip and the lead frame, it is customary to use a form of a degreasing operation, such as immersing the lead frames in freon. Due to the extreme chemical activity of aluminum, the parts, after removal from the freon, become or remain coated with thin films of aluminum oxide, which limit the pull strength of the wire bonds made thereto.